People sure talk a lot about heat pumps, but from what I read, they're best suited to around 10 C, which in my climate is a brief interval between the seasons c

People sure talk a lot about heat pumps, but from what I read, they're best suited to around 10 C, which in my climate is a brief interval between the seasons changing and hardly requires heat at all. It may be two or three times as efficient, in a sense, but if it's not usable all winter, it can't save much energy, can it?